1. Field of the Invention
This invention relates to microwave chokes for power supplies in electronic amplifiers, signal generators, and filters.
2. Description of Prior Art
Microwave chokes are used to block microwave energy from power supplies in amplifiers, signal generators, and filters. Laser drivers for fiber optic cables also require chokes between their power sources and the lasers. Broadband active filters require broadband chokes. If microwave energy leaks into a power supply, the powered device will not function properly. Microwave chokes typically operate within a narrow band of operating frequencies. However, the fiber optic cables now used in cable television and internet communication typically have extremely large band widths and require amplifiers which will amplify signals for all of the frequencies being transmitted over these cables.
In order to cover the broad spectrum of frequencies, multiple narrow band amplifiers are usually employed, each covering a small segment of the frequency range. These amplifiers are operated in parallel. All of the devices used in these amplifiers would generally function over the entire frequency range except for the chokes. If a broadband choke were available, a single broadband amplifier could replace several narrow-band amplifiers.
Until recently, the highest operating frequency of available broadband chokes was only 3 or 4 GHz. These chokes generally had a conventional geometry such as a solenoid or a toroid, and used an air, iron, or ferrite core. Beyond this frequency range, multiple small solenoids were typically used, but these devices have a narrow frequency range of about 10% of the center frequency of operation.
Prior leadless carriers for broadband chokes used a ceramic substrate material with wraparound connections. However, such a carrier design introduces the dielectric properties of the carrier into the performance of the choke. Additionally the prior carriers have metallic pads for connection of the leads, and these pads add substantial capacitance and dielectric losses. This prior carrier design is marginally useable up to 8 GHz with the new broadband conic inductor described herein. However, high frequency performance requires a different approach to the leadless carrier.
The objectives of the present invention are provision of a wideband microwave choke that attenuates electrical signals in frequencies from 300 kHz to 40 GHz with a substantially flat frequency response in this range, or in a band chosen by design within this range, has a protective, totally non-conductive carrier that assists in precise positioning and bonding of the choke to a miniature conductor strip on a circuit board, takes minimal space along the conductor strip, enables fully automated positioning and mounting of the choke on a circuit board by machine, and provides frequency response equal to the choke without a carrier, in a more convenient and easily mountable leadless carrier.
The objectives of the present invention are achieved by a thin, electrically conductive wire 2 wound into a single-layered hollow conic coil 1, having a small end 4 and a large end 5. The coil is mounted in a thin-walled carrier 21 of insulating material such as plastic, with no metallic parts. The carrier holds the coil at an optimum orientation relative to the mounting surface of a circuit board to minimize electromagnetic reflections and resonance that would degrade microwave performance. The small end of the coil 4 is positioned adjacent a contact strip 17 on the circuit board. The wire lead 2 exits tangentially from the small end of the coil and is bonded directly to the contact strip without intermediate metallic pads. An optional cylindrical extension 6 on the large end of the coil provides increased low frequency inductance. The wide range of small to large diameters of coil windings, and careful elimination of sources of electromagnetic interference, reflections, and resonance, provides an inductor that blocks a broad band of radio frequency energy while providing a direct current to pass through the coil unattenuated.